Over the weekend, we got a number of reports that Apple has downgraded the SATA controller in the latest MacBook Pro 13-inch and 15-inch update, capping potential drive speeds. Going over the evidence, it looks like they were right. UPDATED

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The issue has been examined at length in the MacRumors forums, where dozens of users are sharing their experiences, benchmarks and varying levels of disappointment. Here are the kinds of numbers they're finding with faster SSDs (excerpted):

Older 13" MBA, 13" MB, 17" MBP (and old versions of 13"/15" MBP):

Sequential READ = 225 MB/sec
Sequential WRITE = 180 MB/sec

New 13" MBP, 15" MBP

Sequential READ = 115 MB/sec
Sequential WRITE = 95 MB/sec

This sounds terrible: the potential read speeds on the new MacBook Pros have essentially been cut in half. In real-world scenarios, though—particularly Apple-sanctioned real-world scenarios—the speed differences shouldn't matter much; since the MBPs ship HDDs that aren't quite fast enough to max out a 1.5Gb interface, the issue will go unnoticed by most users.

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The problem, though, is with upgrades: there are SSDs on the market that can reach and pass the 1.5GB/s threshold, and in the near future they'll become much more common, and cheaper. There's speculation that this could be remedied with a firmware update, but many are saying this is unlikely; after all, reverting to an older firmware wouldn't have saved Apple any money, while reverting to cheaper hardware could have, albeit barely.

First of all, I believe that NVIDIA has never produced a single GeForce 9400M motherboard chipset (aka ION) that doesn't handle SATA-2 (3Gbps). And even if they did, it would not really save a buck on the chip, as long as the chip size is identical. Most importantly, a 1.5 Gbps SATA-I Geforce 9400M chipset does not exist, as far as I know.

Then what happened? We're not sure, but consider these scenarios: what if some computer shipped with a SATA-I disk? What if 1.5Gbps consumes less power? Because the hardware supports SATA-II, there is a slight chance that this can be updated in the future. We'll be waiting for an official statement from Apple.